For a network with multiple network elements, each network element runs a particular version of software along with a specific configuration for that software. Periodically, the software and/or the configuration of one or more of the network elements are updated. Sometimes, the software and/or configuration updates leads to poor performance or disruption because of problems with the software configuration, incompatibilities between different software configurations on different network elements, loss of connectivity due to incorrect Virtual Local Area Network (VLAN) membership change on a port, incorrect Access Control List (ACL) entry, incorrect route metric change, or other types of problems.
In one example, the network element is upgraded to a new software image to add new features and/or fix problems with the current software image. Alternatively, the network image can be downgraded to a previous version of the software image. To change the software image, the network element loads the new software image, marks this new software image as the current software image, and reboots the network element. As the network element boots up, the new software image is loaded and programs the control and data planes of the network element.
A problem with this way of upgrading or downgrading the software image is that, by rebooting the network element, the network element is inoperable for a relatively long time. For example, rebooting the network element can cause the network element to be off-line for upwards of five minutes. During this off-line time, the data processing functions of the network element are inoperable. This can lead to an interruption of data networking services that rely on the network element.